The invention relates to a method for preparing a vinyl polymer-polyolefine composite, in which from about 10 to about 200 parts of weight of vinyl monomer and from about 0.01 to about 4.0 parts of weight of a free radical polymerization initiator, based on 100 parts of weight of vinyl monomer, are impregnated in 100 parts of weight of polyolefine particles by slowly blending these at a temperature from about 20.degree. to about 130.degree. C. without water by maintaining the particle structure of the polyolefine. In this method, from about 80 to about 1000 parts of weight of suspension water are added, based on 100 parts of the combined weight of polyolefine and vinyl monomer, as well as a stabilizing agent. Thereafter, before the temperature of the aqueous suspension is increased in order to polymerize the vinyl monomer.
The present invention further relates to a new way of preparing a polyolefine composite, which can be applied to be used as such and processed into various articles, e.g., as foamed plastic, as compatibilizer, or as a component in semiconducting layers on electric cables. The composite is comprised of a polyolefine and a vinyl polymer, and the invention relates in part to the preparation of this composite by polymerizing the vinyl monomer inside the polyolefine particles.
For improving rigidity, dimensional stability, adhesion properties against other polymers and materials, printability and the like of polyolefines, which are to be worked into various articles or which are to be foamed into foamed plastic, attempts have been made to blend the polyolefine with some vinyl polymer. Because different polymers often are incompatible with each other, it has however appeared to be difficult to achieve homogeneous blends with an attractive appearance and good physical properties.
In order to avoid these problems, attempts have been made to polymerize the vinyl monomer inside the polyolefine particles. Basically two different methods of polymerizing the vinyl monomer in situ in the polyolefine particles have been suggested, and both methods are based on the fact that the vinyl monomer is allowed to diffuse into the polyolefine particles, after which the polymerization of the vinyl monomer occurs. The greatest difference between the two methods is the way in which the vinyl monomer is allowed to diffuse into the polyolefine particles.
West German patent DE 29 08 662 describes the polymerization of styrene in situ in several different polyolefines. In this method, styrene is added slowly into a water suspension containing polyolefine particles at an elevated temperature. Impregnation and polymerization of the styrene occur simultaneously with the result that the polymerization tends to occur more in the surface regions of the polyolefine particles, which results in that the polystyrene is concentrated on the surface layer of the polyolefine particles.
U.S. Pat. No. 4,412,938 describes the polymerization of styrene in situ in an ethylene vinyl acetate copolymer. In this method, all of the styrene is added at a time into a water suspension containing ethylene vinyl acetate copolymer particles. The styrene is added at so low a temperature that no polymerization occurs. Only after all styrene or most of the styrene has diffused into the ethylene vinyl acetate copolymer particles, the temperature is increased and the polymerization starts. A disadvantage of this method is that it is time-consuming because it takes several hours until the styrene has diffused into the ethylene vinyl acetate copolymer particles.